This invention pertains to dynamic earth anchors, or rock stabilizing fixtures, as the same are also identified, and in particular to sleeves for use in such earth anchors.
Dynamic earth anchors, or rock stabilizing fixtures, are well known. Exemplary thereof, and incorporating the use of a sleeve, is the "Dynamic Rock Stabilizing Fixture" set forth in U.S. Pat. No. Re 32645, and issued to James J. Scott.
The fixture in the aforesaid patent comprises a sleeve having a hollow body which is inserted into the end of a terrestrial borehole, and a roof bolt which is then inserted into the borehole-seated sleeve. Typically, the bolt will have threads or other disruptions on the surface thereof to enhance its fast engagement with the sleeve. The combination sets up an almost immediate restraint of the terrestrial formation, and accommodates a roof plate, or the like, at the formation face. Due to the discontinuities and/or asperities in the sleeve-receiving borehole, it is frequently difficult to set the sleeve into the termination of the borehole.
A practical limitation of the aforesaid patent is that, as the required wall thickness of the sleeve or tube increases to accommodate increased annular space between the rod and the wall of the hole in a geologic formation, one or more of the following conditions will exist:
The body cannot be configured as an overlapped tube because:
1. The rigidity and resilience of the thick tube wall resists overlapping. PA1 2. The inner diameter of the overlapped tube becomes too small to permit penetration by the rod. PA1 3. The wall thickness of the tube needed to create proper interference becomes greater than 1/3the diameter of the borehole making it impossible to place the overlapped tube, which will have a minimum diameter of three times the wall thickness in the borehole. PA1 1. Prevent entry of the rod into the diameter of the tube.
The wall thickness of a continuous tube will either:
2. Possess strength sufficient to prevent expansion of the tube to fill the annulus.
The radial expansion of a tube which is split will cause a "C" shaped opening in the cross-section of the tube in the direction of the split creating a loss of radial confinement of the rod, a reduction in compression of the tube, and a resulting degradation of an anchor performance.
The foregoing illustrates limitations known to exist in present devices. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.